1. Field of the Invention
The present invention relates to a method for manufacturing modified wood by high pressure steam treatment.
2. Description of Related Art
Conventionally, the modification of wood by various chemical treatments has been researched. For example, Hiroyuki Yano, et al. disclose in xe2x80x9cThe Journal of Wood Science, Vol. 38, No. 12, p. 1119-1125 (1992)xe2x80x9d published by the Japan Wood Research Society that wood is modified by soaking in a resorcinol aqueous solution, air-drying the soaked wood, and heating the dried wood in formaldehyde vapor, and thereby, a decrease in loss angle (tan xcex4), an improvement of strength, a reduction in hygroscopicity, improvement of dimensional stability, and the like are achieved.
Furthermore, in addition to the above method, the following treatments are also carried out to modify wood: (1) formalization, (2) acetylation, (3) a treatment by low molecular weight phenol resin, (4) a treatment by resorcin-formaldehyde, and (5) a treatment by saligenin.
The treatment conditions therefor are as follows.
In the formalization, the agents used are tetraoxane and sulfur dioxide, and the treatment conditions are 24 hours at 120xc2x0 C. In acetylation, the agent used is acetic anhydride, and the treatment conditions are 24 hours at 120xc2x0 C. In the treatment by low molecular weight phenol resin, the agent used is low molecular weight phenol, and the treatment conditions are 48 hours (soaked in the low molecular weight phenol) at 160xc2x0 C., and three hours for curing. In the treatment by resorcin-formaldehyde, the agents used are resorcin and paraformaldehyde, and the treatment conditions are 24 hours at 120xc2x0 C. In the treatment by saligenin, the agent used is orthomethylolphenol, and the treatment conditions are 24 hours at 120xc2x0 C.
However, the use of chemicals in any treatment method affects the environment and the human body. Furthermore, since the treatment steps are not simple and require a long time, costs are large. Moreover, in these methods, since a functional group is introduced into the cellulose in the wood or a resin or the like is filled into the cavities in the wood, the weight and density of the wood after treatment tends to increase. As the density of the wood increases, the conversion efficiency of sound decreases, and therefore, when the wood is used as a material for musical instruments, it can be a negative factor.
An object of the present invention is to obtain a method for manufacturing modified wood, which is preferably used as a material for musical instruments, in which the treatment steps are simple, chemicals are not used, and the wood after treatment has good acoustic properties.
To solve the above problems, an aspect of the present invention is to provide a method for manufacturing modified wood comprising a step of retaining wood for 1 to 60 minutes under high pressure steam of 0.2 to 1.6 MPa at 120 to 200xc2x0 C.
The optimum conditions for the high pressure steam treatment are determined by the desired degree of the treatment, the kind of wood, the dimensions of wood, and the like.
Furthermore, another aspect of the present invention is to provide a musical instrument made from the modified wood obtained by the above method as a soundboard or other parts.
According to the method of the present invention, since chemicals such as formaldehyde are never used, there is no effect on the environment or the human body. Furthermore, since treatment steps are simple and require a short time to complete, production costs are decreased.
Furthermore, since cellulose chains in the wood are partially hydrolyzed and rearranged, residual strain in the wood is resolved and the degree of crystallinity increases. Therefore, a modified wood having a superior dynamic modulus of elasticity (E) and oscillation properties such as damping factor of oscillation (tan xcex4) can be obtained. The above change is similar to the change in wood which occurs with the passage of time of some hundred years, therefore, it can be said that the modified wood of the present invention is antiquated in the above treatment.
Moreover, since the wood becomes dark brown by the above modification and the contrast of grain is increased, the modified wood can be developed with a transparent and deep appearance while the coating step can be shortened.
In particular, the above modified wood is preferably used as a material for musical instruments.